1. Field of the Invention
This invention relates to a device to retrofit a valve such as an alfalfa valve, without modification of the valve, to convert it from manual to pneumatic control and provide means for closure of the valve if operating pressure to the system is interrupted.
2. Description of the Art
In irrigation systems, the flow of water to furrows, fields, or other selected areas is controlled by valves which release water automatically or by manual control from irrigation pipelines. Most devices applicable to irrigation systems which used buried irrigation pipelines rely on inflatable bladders or diaphragms, in contact with the flowing irrigation stream, and actuated by hydraulic or pneumatic pressure. About 30 to 40% of all surface irrigated acreage in the United States involves the use of alfalfa valves. FIG. 4 shows a manually controlled alfalfa valve used to regulate water flow from a pipe (29) which contains irrigation water under low pressure. An alfalfa valve consists of a threaded stem (32) carrying a circular dish-shaped cover (25). Stem 32 is secured to cover 25 through threaded hole 36 in the center of cover 25 and is screwed into a threaded nut (28) supported by radial arms (27). Pipe 29 has a valve mount (flange 26) fastened at its top. The valve is designed so that when cover 25 is secured against flange 26, water is prevented from flowing out of the pipe. To operate, handle 33 on stem 32 is rotated so that cover 25 is pushed against flange 26 to prevent the flow of water out of pipe 29 or raised from flange 26 to allow water to flow out of the pipe.
Haise et al. (U.S. Pat. No. 3,320,750) describes a pneumatically operated irrigation system for use in conjunction with an alfalfa valve. In this system, an inflatable member is positioned between cover 25 and flange 26 such that when the member is inflated, water is prevented from flowing out of the pipe 25, and when the inflatable member is deflated, water is allowed to flow out of the pipe and irrigate the field being served. This system can be controlled automatically by use of timers or electrical circuits which cause the valve to be opened or closed.
A serious problem with devices which use inflatable bladders or diaphragms to control irrigation equipment is that the devices have the characteristic of opening if the source of the operating pressure is interrupted, either intentionally as part of the irrigation operation or unintentially by malfunction of the system. As a result, malfunctions can cause expensive and sometimes disastrous inundations of water onto the field.
While pneumatic valves which operate so that interruption of operating pressure closes the valve, no device is available to readily convert an alfalfa valve to a pneumatic valve and provide a means for closure of the valve if the control pressure to the system is interrupted.